The present invention relates generally to fluorinated and non-fluorinated base materials or substrates having oxyfluorinated surfaces which can be reacted with other functionalities, such as organosilanes.
Fluorinated polymers, such as fluorohydrocarbon polymers, e.g. polyvinylidene fluoride, polyvinyl fluoride (PVF), including the well known fluorocarbon polymers, e.g., perfluorinated materials, such as PTFE, are characterized by extreme inertness, high thermal stability, hydrophobicity, and a low coefficient of friction as to resist adhesion to almost any material. While these properties are highly desirable, it would also be advantageous to modify some of the polymers' characteristics in order to expand the scope of their useful applications. For instance, in the field of biocompatible materials fluorocarbon polymers in various forms have been developed. But, because of their chemical inertness and extremely low reactivity the scope of improved devices, such as implantable prosthetic devices and probes has been limited. In the field of membranes and filters, fluoropolymers have also had limited applications due to low surface energy problems associated with these materials. Membranes and filters fabricated from PTFE, for example, are unable to selectively inhibit permeation of liquids with high surface tensions (&gt;50 dynes/cm) while allowing liquids having lower surface tensions to pass through. PTFE has also been under intense study for applications in cell culture growth membranes, but a principal shortcoming has been the inability of cells to adhere to this low energy material.
Efforts of others to modify the properties of fluoropolymers have not been totally satisfactory. U.S. Pat. 4,548,867 (Ueno et al), for example, discloses a fluorine-containing synthetic resin having improved surface properties as evidenced by increased wettability with water, printability and susceptibility to adhesive bonding. The fluoropolymer is exposed to a low temperature plasma comprising an organic nitrogen-containing gas. Instead of modifying the atomic composition of the fluoropolymer starting material, Ueno et al form a thin "layer" of a nitrogen-containing wettable material thereto. Consequently, the adherence of such an overcoating tends to alter the microstructural morphology of the original polymer, especially with respect to pore size. This coating also alters desirable surface properties exhibited by the original fluorinated material.
Others have attempted the use of glow discharge and corona treatments to produce surface modifications. In some early work, Schonhorn and Hansen found that exposure of polyolefins and perfluorinated polymers to low power radio frequency electroless discharges in inert gas atmospheres produced favorable results over wet chemical methods. Their improvement in the bondability of surfaces was limited and attributed to the formation of a highly cross-linked surface layer. Studies of Hollahan et al, J. Polym. Sci., 13, 807 (1969) aimed at rendering polymer surfaces biocompatible included the interaction of PTFE with plasmas excited in ammonia and nitrogen/hydrogen mixtures, the goal being the introduction of amino groups into the polymer surface. However, the long exposure times and high powers employed provided only limited results, and further, are taught to have produced significant changes not only in the surface chemistry, but also in the native bulk properties. Morphology of the surface was also severely effected.
In another ESCA study entitled "ESCA Study of Polymer Surfaces Treated by Plasma" Yasuda et al, J. Polym. Sci., Polym Chem. Ed., 15, 991 (1977) the effects of discharges in argon and nitrogen on surface chemistry were considered on a range of polymers. PTFE was found to be particularly susceptible to defluorination and the introduction of oxygen and nitrogen moieties into the surface. Accordingly, there is a need for permanently modified homogeneous fluorinated polymers in which some of the original fluorine functionality is eliminated and replaced with oxygen functionality and hydrogen bonded to the carbon polymer backbone while substantially preserving the original surface morphology and bulk characteristics of the unmodified material on a molecular scale.
A further manifestation of the inert characteristics of highly fluorinated polymers has been their resistance to enter directly into reactions with other substances for purposes of introducing other functionalities and developing new properties not normally found in fluoropolymers. It has also been discovered that when fluoropolymers are exposed to radio frequency glow discharge (RFGD) in the presence of hydrogen gas-vapor (water, methanol or formaldehyde) mixture, a modified surface forms comprised of a controllably reduced amount of original fluorine with controlled amounts of hydrogen and oxygen or oxygen-containing groups covalently bonded to the carbon backbone of the polymer. The modified oxyfluoropolymers retain the unique properties of highly fluorinated polymers, such as PTFE, with the tendency to repel water and other polar solvents, high thermal stability, low adhesion and friction coefficients. However, unlike the modifications observed by Andrade et al (U.S. Pat. 4,508,606) and Ueno et al (U.S. Pat. 4,548,867) it has been found that the oxyfluoropolymers have reactive chemical sites which permit bonding with other chemical functionalities, such as organosilanes to form a class of novel and useful refunctionalized fluoropolymers. Accordingly, there is need for a series of novel and useful fluoropolymers having their surfaces oxyfluorinated and refunctionalized.
The foregoing oxyfluoropolymers impart a wide range of different and useful surface chemistries to the base fluoropolymer by enabling one to incorporate and/or fabricate sensor devices such that the non-stick, low energy properties of the base fluoropolymer substrate are preserved. The processes utilized for their manufacture have proven to be technologically simple to facilitate while enabling fabrication of devices which, for instance, are non-fouling and resistive to corrosion and/or weathering while simultaneously providing sensitivity to specific and selective molecules, biology or chemistry in a given environment. Representative examples include antibody based fiber optic devices for determining specific antigen concentrations in biologically diverse media, as well as protein and cell culture templates for adhesion and proliferation studies.
Ideally, it would be desirable to expand these capabilities to a broader range of materials which might already be in use in various technological areas, but are non-fluorinated. The problem, however, with refunctionalizing non-fluorinated materials is that often there is no simple, low cost direct route for producing a well defined and controlled interfacial modification equivalent to that produced with fluoropolymers. Such being the case, there is a need for non-fluorinated substrates and methods of manufacture which would include treatment for the addition of fluorine or fluorocarbon coatings thereto which are suitable for the addition of hydroxyl functionality, and which may also be refunctionalized.
In some instances, it may also be desirable to preserve the surface characteristics of the non-fluorinated substrates, for example, in conjunction with well defined boundaries or regions, e.g., stripes or patterns, while applying specific functional chemistries. Thus, the present invention also contemplates utilizing known masking techniques whereby fluorocarbon coatings are applied only to desired regions of the substrate with preferred dimensions ranging from 0.5.mu. or greater. Through known masking techniques regions of the substrate can be selectively defluorinated and refunctionalized according to methods previously disclosed without inducing changes throughout the entire substrate bordering these refunctionalized areas.
As a further extension of masking technology, in the field of electronics the ability to pattern electrical conduits and circuitry at the submicron level has become a major industry. This has been demonstrated almost exclusively, however, on ceramic and metallic materials which due to high dielectric constants and high surface energies are complicated with static charge build-ups resulting in current cross-talk and surface corrosion. The ability to utilize, for example, low dielectric materials, such as PTFE and FEP would advantageously reduce these problems and provide a significant technological advance in the field of high frequency, microwave microelectronics. But, due to economics and technical difficulties in processing fluoropolymers, such applications are likely to be restricted to highly specialized uses.
Both the economic and technical problems in this field of electronics can be bridged via the methods disclosed herein. That is, by modifying the fluorocarbon coatings applied to substrates by oxyfluorination and refunctionalization substrates can be formed for which processing and utilization are common in the electronics industry, but with the added benefit of a fluorocarbon based film with desirable dielectric and corrosion resistant properties.